1. Field of the Invention
This invention relates in general to the use of a schlieren optical system in combination with a television camera and video signal processing equipment for the examination of specimens containing parts which have different refractive indexes. More particularly, this invention relates to the use of such method and apparatus for obtaining population and/or profile data of bodies contained within a transparent mass. The bodies may be transparent or otherwise not distinguishable by the unaided eye, which are contained within a transparent mass.
This invention is particularly useful in quality control techniques in the production of chemicals. For example, transparent polymers often contain transparent particles or bodies which are indistinguishable by the unaided eye. These bodies may be residues from raw materials, foreign bodies, or perhaps malformed portions of the polymer itself. Such bodies are particularly objectionable in solutions or melts of the polymer when spinning or casting operations are undertaken. By examination of such bodies, which normally cannot be seen by the unaided eye using conventional techniques, the population and profile data will allow quality determinations to be made. Also, such data will likely lead to the identity of such bodies so steps can be taken to eliminate them. By use of the population and profile data derived by the present invention, it is possible to determine accurately the quality of a particular specimen, study the causes of poor quality material and possibly eliminate such causes. Examination of other specimens using this method and apparatus will be apparent to those skilled in the art.
2. Description of the Prior Art
In the manufacture of certain products formed from polymers such as cellulose acetate, vinyl chloride, and other polymers which are soluble in organic volatile solvents, difficulty is frequently encountered with portions of the polymer which are not fully soluble in the solvent. These portions tend to swell in some instances, or in other instances they become only partially dissolved, forming gels suspended in the polymer solution. Large portions can be detected and removed by conventional techniques, but the smaller portions tend to interfere with normal manufacturing operations, frequently stopping up holes in extrusion nozzles used to form fibers, or producing hard lumps in the surface of sheeting materials formed from the polymer.
Schlieren optical systems are well known in the art and have been used for observing phenomena involving optical-path differences which result in light beam deflections such as, for example, the checking of mirrors wherein the optical-path differences derive from defects in the mirror, or the analysis of fluid flow in wind tunnels wherein a model is immersed in a gas stream and the optical-path differences derive from the refractive-index variations related to pressure variations. The principle used in observing these phenomena is that the light rays passing through the object being observed are deviated by different amounts depending on the refractive index gradient, which corresponds to the concentration gradient.
Patents relating to schlieren optical systems and/or uses thereof include U.S. Pat. Nos. 3,847,484 and 3,767,306. Also of interest is Krosovskii et al, "The Sensitivity Threshold of an Autocallination Television Shadow-Graph," Sov. J. Opto Technol., Vol 41, No. 9, September, 1974, p. 406-409 and and C. L. Strong, "A Laser Beam and a Photocell are Used to Measure the Dirt Content of Water," The Amateur Scientist. U.S. Pat. No. 3,847,484 discloses laser light used in a schlieren system for studying the distribution of molecular density in solution under the influence of a centrifugal force, and the Krasovskii et al article relates to television shadowgraphs used for studying transparent optical media.